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Physics 112 Midterm Exam Questions and Collect Answers
(100% Verified) |Latest Version 2025/2026
If two objects both have more of the positive type of charge than negative (usually
referred to as a positive net charge)
then the objects will repel each other.
If two objects both have more of the negative type of charge than positive (referred to
as a negative net charge)
then the objects will repel each other.
If one object has more of the positive type of charge and one object has more of the
negative type of charge
then the objects will attract each other.
If a material gains electrons
the material will have a negative net charge
If a material loses electrons
the material will have a positive net charge.
A particular object has a net 6.5 μC of the positive type of charge. Were electrons
transferred onto or off the object? How many?
Since the object has extra of the positive type of charge, electrons must have been
transferred off the material. Since electrons carry the negative type of charge, removing
electrons would have left behind more positive than negative.
The total amount of charge moved off the material was 6.5 μC. Each electron moved off
carries 1.6x10-19 C. Convert μC into C and divide.
6.5x10-6 C / 1.6x10-19 C = 4.06x1013 electrons were removed.
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Solve for the number of charge carrier particles (protons or electrons) transferred on
or off the object.
The amount of charge carried by one electron is 1.6x10-19 C. Divide the total charge by the
charge of one electron to solve for the number of electrons.
(3.5x10-6 C) / (1.6x10-19 C) = 2.25x1013 electrons were transferred off the object.
conductors
Materials that allow electrons to move easily through them. Metals are good conductors
insulators
Materials that do not allow electrons to move freely through them. Nonmetals are good
insulators
Semiconductors
are a class of materials that, as you might expect, share properties of both.
Conduction
is the movement of charge from one object to another. It is easy to move charge from metal
to metal (conductor to conductor) but much more difficult to move charge from insulator to
insulator.
The transfer of charge caused by rubbing two objects against each other is a special type of
conduction called triboelectric charging.
An electroscope is a device that has small gold foil strips suspended from a metal rod.
If a negatively charged rod is brought near the top of a neutral electroscope, the gold
foil strips will separate. (See below.) Explain why this happens.
The negative charge on the rod repels the negative charge already present in the
electroscope. Since the electroscope is made from metals, electrons will be pushed down
into the gold strips. The electroscope is now polarized (the top is more positive, and the
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bottom is more negative). However, the relocated negative charge now in the thin gold
strips will repel each other causing the gold strips to separate.
Induction
is a charge transfer process that involves polarizing an object and then allowing charge to
transfer to another object through conduction. While still under the influence of the dipole,
the charge transfer mechanism is removed (the two objects are moved apart). The two
objects are now charged.
Polarization
is a redistribution of charge rather than a transfer of charge; the total amount of charge on
the polarized object does not change.
static electric force
Proportional to the quantity of net charge on both objects, and proportional to the inverse-
square of the distance between the two charged objects.
In other words:
Fe α q1q2 / r2
Where Fe is the force, q1 and q2 are the net charges on the object, and r is the distance
between the two objects.
The distance d between two positively charged particles is measured. The distance
between the two particles is increased to 2d. If the original electrostatic force
between the objects was F, what is the new force?
Force has an inverse-squared relationship with distance. If the distance is doubled, then
the force will change by a factor of (1/2)^2 = ¼. In other words, the new force will be four
times smaller.
Since the two particles are both positive, the force will be a repelling force.
Fe = kq1q2/r2
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This constant is called the Coulomb's law constant, and has a value of 9x10^9 N-m2/C2.
What is the static electric force between a -3.0 μC charge and a +6 μC charge if they
are 2.0 cm apart?
F = kqq/r^2
F = (9x10^9 N-m2/C2)(3x10^6 C)(6x10^6 C) / (0.02 m)^2
F = 405 N
What if you have more than two charged particles?
Sketch the system if a drawing is not provided.
Draw and label a free body diagram.
Calculate all the forces.
Solve for any x and y force components.
Add all the x direction forces together, and then add all the y direction forces together.
Use the Pythagorean theorem to combine the components into their vector form.
Use arctangent to solve for the direction of the final vector form.
Particle A has a net charge of +4 mC, and is located at coordinate position (0, 2) m.
Particle B has a net charge of -2 mC, and is located at coordinate position (0, 0) m.
Particle C has a net charge of +6 mC, and is located at position (3, 0) m.
What is the net charge on particle B? Ignore any gravity effects.
F = kqq/r2F
a on b = (9x109 N-m2/C2)(4x10-3 C)(2x10-3 C) / (2 m)2F
a on b = 18,000 N
F c on b = (9x109 N-m2/C2)(6x10-3 C)(2x10-3 C) / (3 m)2F
c on b = 12,000 N
Since these forces don't have any angles, you don't need to solve for their x and y
components. Solve for the net force and the direction of the net force.
ΣF2 = Fy2 + Fx2
ΣF2 = (18,000 N)2 + (12,000 N)2
Physics 112 Midterm Exam Questions and Collect Answers
(100% Verified) |Latest Version 2025/2026
If two objects both have more of the positive type of charge than negative (usually
referred to as a positive net charge)
then the objects will repel each other.
If two objects both have more of the negative type of charge than positive (referred to
as a negative net charge)
then the objects will repel each other.
If one object has more of the positive type of charge and one object has more of the
negative type of charge
then the objects will attract each other.
If a material gains electrons
the material will have a negative net charge
If a material loses electrons
the material will have a positive net charge.
A particular object has a net 6.5 μC of the positive type of charge. Were electrons
transferred onto or off the object? How many?
Since the object has extra of the positive type of charge, electrons must have been
transferred off the material. Since electrons carry the negative type of charge, removing
electrons would have left behind more positive than negative.
The total amount of charge moved off the material was 6.5 μC. Each electron moved off
carries 1.6x10-19 C. Convert μC into C and divide.
6.5x10-6 C / 1.6x10-19 C = 4.06x1013 electrons were removed.
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Solve for the number of charge carrier particles (protons or electrons) transferred on
or off the object.
The amount of charge carried by one electron is 1.6x10-19 C. Divide the total charge by the
charge of one electron to solve for the number of electrons.
(3.5x10-6 C) / (1.6x10-19 C) = 2.25x1013 electrons were transferred off the object.
conductors
Materials that allow electrons to move easily through them. Metals are good conductors
insulators
Materials that do not allow electrons to move freely through them. Nonmetals are good
insulators
Semiconductors
are a class of materials that, as you might expect, share properties of both.
Conduction
is the movement of charge from one object to another. It is easy to move charge from metal
to metal (conductor to conductor) but much more difficult to move charge from insulator to
insulator.
The transfer of charge caused by rubbing two objects against each other is a special type of
conduction called triboelectric charging.
An electroscope is a device that has small gold foil strips suspended from a metal rod.
If a negatively charged rod is brought near the top of a neutral electroscope, the gold
foil strips will separate. (See below.) Explain why this happens.
The negative charge on the rod repels the negative charge already present in the
electroscope. Since the electroscope is made from metals, electrons will be pushed down
into the gold strips. The electroscope is now polarized (the top is more positive, and the
, Page |3
bottom is more negative). However, the relocated negative charge now in the thin gold
strips will repel each other causing the gold strips to separate.
Induction
is a charge transfer process that involves polarizing an object and then allowing charge to
transfer to another object through conduction. While still under the influence of the dipole,
the charge transfer mechanism is removed (the two objects are moved apart). The two
objects are now charged.
Polarization
is a redistribution of charge rather than a transfer of charge; the total amount of charge on
the polarized object does not change.
static electric force
Proportional to the quantity of net charge on both objects, and proportional to the inverse-
square of the distance between the two charged objects.
In other words:
Fe α q1q2 / r2
Where Fe is the force, q1 and q2 are the net charges on the object, and r is the distance
between the two objects.
The distance d between two positively charged particles is measured. The distance
between the two particles is increased to 2d. If the original electrostatic force
between the objects was F, what is the new force?
Force has an inverse-squared relationship with distance. If the distance is doubled, then
the force will change by a factor of (1/2)^2 = ¼. In other words, the new force will be four
times smaller.
Since the two particles are both positive, the force will be a repelling force.
Fe = kq1q2/r2
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This constant is called the Coulomb's law constant, and has a value of 9x10^9 N-m2/C2.
What is the static electric force between a -3.0 μC charge and a +6 μC charge if they
are 2.0 cm apart?
F = kqq/r^2
F = (9x10^9 N-m2/C2)(3x10^6 C)(6x10^6 C) / (0.02 m)^2
F = 405 N
What if you have more than two charged particles?
Sketch the system if a drawing is not provided.
Draw and label a free body diagram.
Calculate all the forces.
Solve for any x and y force components.
Add all the x direction forces together, and then add all the y direction forces together.
Use the Pythagorean theorem to combine the components into their vector form.
Use arctangent to solve for the direction of the final vector form.
Particle A has a net charge of +4 mC, and is located at coordinate position (0, 2) m.
Particle B has a net charge of -2 mC, and is located at coordinate position (0, 0) m.
Particle C has a net charge of +6 mC, and is located at position (3, 0) m.
What is the net charge on particle B? Ignore any gravity effects.
F = kqq/r2F
a on b = (9x109 N-m2/C2)(4x10-3 C)(2x10-3 C) / (2 m)2F
a on b = 18,000 N
F c on b = (9x109 N-m2/C2)(6x10-3 C)(2x10-3 C) / (3 m)2F
c on b = 12,000 N
Since these forces don't have any angles, you don't need to solve for their x and y
components. Solve for the net force and the direction of the net force.
ΣF2 = Fy2 + Fx2
ΣF2 = (18,000 N)2 + (12,000 N)2
